Vapor phase conversion of molybdenum or tungsten compound to form the oxide or metal



May 5, 1970 w. E. BRUSH 3,510,291

VAPOR PHASE CONVERSION, OF MOLYBDENUM OR TUNGSTEN COMPOUND I TO FORM THE OXIDE OR METAL Filed Nov. 10, 1966 PREPARE AQUEOUS SOLUTION OF AMMONIATED TUNGSTEN COMPOUND OR MOLYBDENUM COMPOUND ATOMIZE SOLUTION INTO CHAMBER HEATED TO TEMPERATURE OF AT LEAST 400C AND HAVING A CONTROLLED ATMOSPHERE United States Patent 3,510,291 VAPOR PHASE CONVERSION OF MOLYBDENUM OR TUNGSTEN COMPOUND TO FORM THE OXIDE OR METAL Walton E. Brush, Pompton Plains, N.J., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennnsylvania Filed Nov. 10, 1966, Ser. No. 593,526 Int. Cl. B22f 9/00 US. Cl. 75.5 6 Claims ABSTRACT OF THE DISCLOSURE Process for rapidly forming finely divided tungsten or molybdenum oxide or metal which comprises preparing an aqueous solution of ammoniated tungsten compound or ammoniated molybdenum compound, and atomizing the solution into a chamber having a predetermined atmosphere and which is heated to and maintained at a temperature of at least about 400 C.

This invention relates to the production of very pure refractory metal powders and their oxides and, more particularly, to a process for rapidly and effectively forming very pure, finely divided tungsten oxide or metal or molybdenum oxide or metal.

In the usual processing of tungsten or molybdenum from the ore, the refractory metal constituent of the ore is ultimately converted to a purified oxide. The oxide is reduced to powdered metal by heating in a hydrogen atmosphere and the powdered metal thereafter processed into ingot form in accordance with standard electrical sintering practices. In the case of tungsten, it is customary to convert the ore to a so-called ammonium paratungstate, which is thereafter heated to convert same to the trioxide. In the case of molybdenum, the ore molybdenite (M is roasted to oxidize the molybdenum and the sublimed trioxide recovered. Various additional, known processing steps are used to purify the materials.

Difiiculties are encountered when converting the molybdenum trioxide to powdered molybdenum, since the trioxide tends to sublime in an uncontrolled fashion. Accordingly, the conversion of the trioxide to the dioxide is normally accomplished in one step and the conversion of the dioxide to the molybdenum metal powder is normally accomplished in a second, separate step, thereby introducing an additional handling step into the processing.

It is the general object of the present invention to provide a simple process for rapidly forming finely divided tungsten or molybdenum oxide or metal.

It is another object to provide a simple and rapid method for producing purified, finely divided tungsten or molybdenum metal or tungsten or molybdenum oxides.

It is a further object to provide a fast and controllable method for producing finely divided tungsten or molybdenum metal or oxides from an ammoniated tungsten or molybdenum compound.

The foregoing objects, and other objects which will become apparent as the description proceeds, are achieved by initially preparing an aqueous solution consisting essentially of ammoniated tungsten compound or ammoniated molybdenum compound. The prepared solution is atomized into a reaction chamber which is heated to a temperature of at least about 400 C. and which chamber contains a predetermined atmosphere.

If an ammoniated molybdate solution is being atomized into the chamber at a chamber temperature of from about 400 C. to 700 C., with the chamber atmosphere comprising oxygen, the resulting product of decomposition will be molybdenum trioxide. If, on the other hand,

3,510,291 Patented May 5, 1970 ice the chamber temperature is from about 400 to 900 C. and the chamber atmosphere is hydrogen, the resulting product which is formed will be molybdenum dioxide. If the chamber temperature is greater than about 900 C. and the chamber atmosphere is hydrogen, the resulting formed product will be finely divided molybdenum metal.

If the solution sprayed into the chamber is an aqueous ammoniated tungstate solution, and the atmosphere in the chamber comprises oxygen, the resulting formed product will be tungsten trioxide. If the chamber atmosphere is neutral, the resulting formed product will be a combination of mixed tungsten oxides which will have the appearance of a so-called blued tungsten oxide. If the chamber temperature is from about 400 C. to 750 C. and the chamber atmosphere is hydrogen, the resulting formed product will be tungsten dioxide. If the chamber temperature is greater than about 750 C. and the chamber atmosphere is hydrogen, the resulting formed product will be finely divided tungsten metal. I

For a better understanding of the invention, reference should be had to the accompanying drawings, wherein:

FIG. 1 is a flow diagram setting forth the basic steps of the present method; and

FIG. 2 is a diagrammatic view, shown partly in section, illustrating an apparatus which can be used to carry out the method of the present invention.

In accordance with the present method and as shown in the flow chart, there is first formed an aqueous solution consisting essentially of ammoniated tungsten compound or ammoniated molybdenum compound. This solution is atomized into a chamber which is heated to a temperature of at least about 400 C. and which has a controlled atmosphere, in order to form the finely divided oxide or metal.

An apparatus 10 which is suitable for practicing the present method is shown in FIG. 2 and comprises a reaction chamber 12 and so-called cyclone separator 14. The reaction chamber 12 is adapted to be heated to a predetermined temperature, preferably by means of electrical heating elements 16. The solution to be atomized into the chamber is introduced through atomizer 18 and the controlled atmosphere within the chamber is introduced through an inlet tube 20. As will be explained in greater detail hereinafter, when the ammoniated molybdate or tungstate solution is atomized into the chamber, it immediately reacts to form either the oxide or the finely divided metal, which drifts or falls downwardly and is fed through connecting conduit 22 to the so-called cyclone separator 14. The majority of the formed oxide or metal is collected in the receiving container 24 and the residual gas passes through outlet conduit 26 and through a final filter 28 before passing through the pump 30. The gas which is introduced into the reaction chamber 12 is passed through a preheater 32 and the gas may be recirculated if desired.

First considering the production of molybdenum oxide or finely divided molybdenum metal, molybdenum trioxide (M00 is a stable, white, crystalline powder having a melting point of 795 C., a boiling point of 1155 C. and a sublimation temperature of about 700 C. Molybdenum trioxide is made commercially by roasting molybdenite (M08 in air and collecting the resulting sublimate.

Molybdenum dioxide (M00 is a lead-gray crystalline powder and is formed by the reduction of the trioxide, or by the partial oxidation of metallic molybdenum. When the trioxide is reduced to the dioxide in hydrogen, there is a tendency to sublime the unreduced trioxide if the reduction is not carefully controlled.

In accordance with the present invention, there is first prepared an aqueous solution consisting essentially of ammoniated molybdenum compound. As an example,

molybdenum trioxide is added to a hydrochloric acid solution, filtered and washed thoroughly with cold water several times, in order to remove any undesired alkalimetal elements. The washed trioxide is then dissolved in ammonium hydroxide and the product can be further purified, if desired, by introducing hydrogen sulphide into this solution. As an example for preparing the ammonium molybdate solution, 1080 ml. of concentrated ammonium hydroxide solution is added to 1960 ml. distilled Water. The resulting ammonium hydroxide solution is stirred vigorously while 500 grams of the washed molybdenum trioxide is added thereto. The solution is then filtered and the purified filtrate is ready to be introduced into the apparatus 10. Alternatively, the filtrate may be further purified by evaporating the ammonium molybdate solution, filtering off the crystals, redissolving the resulting crystals in heated ammonium hydroxide, and filtering again.

In preparing molybdenum trioxide from the ammonium molybdate solution, the solution is atomized into the reaction chamber 12 which preferably contains an atmosphere comprising oxygen maintained at a temperature of from about 400 C. to 700 C. As specific example, an ammonium molybdate solution containing molybdenum in such amount as to provide 15% by weight of the solution of molybdenum trioxide is sprayed into the chamber 12 containing an air atmosphere heated to a temperature of 500 C. The main advantages of this method of preparation of molybdenum trioxide are that the resulting material is very pure, and the reaction is readily controllable and is very rapid.

In order to prepare molybdenum dioxide directly from ammonium molybdate, the aqueous solution is atomized into a chamber which contains a hydrogen atmosphere maintained at a temperature of from about 400 C. to 900 C. As a specific example, an ammonium molybdate solution such as specified hereinbefore is sprayed into a chamber containing hydrogen at a temperature of about 700 C. The dioxide is formed directly from the molybdate solution and the exothermic nature of the reaction involved as the material passes from the trioxide to the dioxide stage does not constitute any problem since the chamber atmosphere constitutes a heat reservoir to absorb generated heat. Thus temperature control is not a problem.

In order to prepare molybdenum metal directly from the molybdate solution, the aqueous molybdate solution is atomized into a chamber containing a hydrogen atmosphere at a temperature greater than 900 C. As a specific example the foregoing ammonium molybdate solution is sprayed into a chamber containing hydrogen of a temperature of about 1050 C. The atomized material reacts immediately to form finely divided molybdenum metal of very pure and finely divided state.

In forming tungsten oxide or tungsten metal in ascordance with the present invention, there is first prepared an ammoniated tungsten compound. In the usual preparation techniques for purifying tungsten from its ores, the tungsten ore is digested and ultimately reacted to form an ammonium paratungstate. This procedure is well known and is a commercial process. To form an ammonium tungstate solution, the ammonium paratungstate crystals can be redissolved in a hot ammoniacal solution containing tungsten in such amount that the amount of equivalent tungsten trioxide consists of by weight of the total solution.

The resulting ammoniated tungsten solution can be used to form tungsten trioxide, an intermediate tungsten oxide, tungsten dioxide or pure tungsten metal, depending upon the temperatures and atmospheres involved in the reacting chamber. If the atmosphere contained within the chamber comprises oxygen, tungsten trioxide will be formed directly when the atomized solution is sprayed into he chamber. As a specific example, the

chamber contains an air atmosphere and is maintained at a temperature of approximately 600 C.

Tungsten also exists in the oxide form as a so-called blued tungsten oxide which comprises a mixture of intermediate oxides such as W O and W O Such a material can be formed in accordance with the present method by maintaining a neutral atmosphere within the chamber, such as nitrogen, when the solution is atomized therein. As a specific example, the atmosphere within the chamber is heated to a temperature of approximately 600 C. The resulting compound will be a blued tungsten oxide.

Tungsten dioxide can also be formed directly from the ammoniated tungstate solution by maintaining a hydrogen atmosphere within the chamber while maintaining same at a temperature of from about 400 C. to 750 C. As a specific example, the foregoing tungstate solution is sprayed into the chamber while it is maintained at a temperature of about 600 C. Tungsten dioxide will be formed directly from the ammoniated tungstate solution.

If the temperature of the chamber is greater than about 75 0 C. and a hydrogen atmosphere is maintained therein, the ammoniated tungstate solution will be reduced directly to very finely divided tungsten metal powder. As a specific example, the chamber and the hydrogen gas are heated to a temperature of 950 C. and the foregoing tungstate solution sprayed therein.

It should be understood that in the foregoing examples, there does not exist a sharp cut-off or transition point with respect to any of the given temperatures. For example, if the ammoniated tungsten solution is sprayed into a chamber which is maintained at a temperature of 750 0, there will be formed both tungsten metal powder and tungsten dioxide. The temperatures as specified, however, do represent general transition temperatures, above and below which there will be a predominance of the indicated oxides or metals.

The above process can be used to produce so-called doped or undoped metals or oxides. As an example, it is customary to dope some types of tungsten with thorium dioxide. This is readily accomplished by dissolving a small amount of thorium nitrate in the ammoniated tungsten solution, which will convert directly to thorium dioxide upon being atomized into the reaction chamber. So-called alkali silicate doping of tungsten can also be incorporated into the powder at the atomizing stage of the preparation. Such materials can be added to the tungstate solution as potassium chloride, potassium silicate and aluminum chloride, for example, and the relative proportions required for these materials are well known in the art. As an example, the residual doping constituents after atomization can comprise 0.3% by Weight potassium, 0.02% by weight alumina and 0.4% by weight silica, all taken with respect to the equivalent tungsten metal which is present.

Aqueous ammoniated tungstate or molybdate solutions of various complex forms have been reported to exist. Any of these will decompose to produce the oxide or metal in accordance with the present invention, and may be substituted for the specific molybdate or tungstate solutions as described hereinbefore.

The foregoing indicated tungsten or molybdenum oxides or finely divided metal can be marketed as such for further processing into the final products, such as wire, welding rods, lamp filaments, etc. This final fabrication is in accordance with well-known powder metallurgy techniques, including the usual compacting of the powder, sintering, and swaging and drawing or rolling.

It will be recognized that the objects of the invention have been achieved by providing a very effective and fast method as well as a method which is economical, controllable and simple for preparing oxides or powders of tungsten or molybdenum.

While preferred embodiments of the invention have been illustrated and described in detail, it is to be particularly understood that the invention is not limited thereto or thereby.

I claim as my invention:

1. The process of rapidly forming finely divided tungsten or molybdenum oxide or metal, which process comprises:

(a) preparing an aqueous solution consisting essentially of ammoniated tungsten compound or ammoniated molybdenum compound; and

(b) atomizing said solution into a chamber having an inert or hydrogen atmosphere in the case of said tungsten compound or a hydrogen atmosphere in the case of said molybdenum compound, and said atmosphere is heated to and maintained at a temperature of at least about 400 C.

2. The process as specified in claim 1, wherein said aqueous solution is an aqueous ammoniated molybdate solution, and said solution is atomized into a chamber containing a hydrogen atmosphere at a temperature of from about 400 C. to 900 C.

3. The process as specified in claim 1, wherein said aqueous solution is an aqueous ammoniated molybdate solution, and said solution is atomized into a chamber containing a hydrogen atmosphere at a temperature greater than about 900 C.

4. The process as specified in claim 1, wherein said aqueous solution is an aqueous ammoniated tungsten solution, and said solution is atomized into a chamber containing an inert atmosphere.

5. The process as specified in claim 1, wherein said aqueous solution is an aqueous ammoniated tungstate solution, and said solution is atomized into a chamber containing a hydrogen atmosphere at a temperature of from about 400 C. to 750 C.

6. The process as specified in claim 1, wherein said aqueous solution is an aqueous ammoniated tungstate solution, and said solution is atomized into a chamber containing a hydrogen atmosphere at a temperature greater than about 750 C.

References Cited UNITED STATES PATENTS 2,966,406 12/1960 Spier et al. ----.5 3,172,753 3/1965 Walsh 75.5 3,236,634 2/1966 Lambdin et a1. 75-.5 3,264,098 8/1966 Heytmeijer 75-2-6 3,415,640 12/1968 Lambert 75-.5

L. DeWAYNE RUTLEDGE, Primary Examiner W. W. STALLARD, Assistant Examiner US. Cl. X.R. 264-5, 13 

